/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.support;

import java.io.IOException;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.ResourceEntityResolver;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationContext;
import org.springframework.core.io.Resource;

/**
 * Convenient base class for
 * {@link org.springframework.context.ApplicationContext} implementations,
 * drawing configuration from XML documents containing bean definitions
 * understood by an
 * {@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader}.
 * 
 * <p>
 * Subclasses just have to implement the {@link #getConfigResources} and/or the
 * {@link #getConfigLocations} method. Furthermore, they might override the
 * {@link #getResourceByPath} hook to interpret relative paths in an
 * environment-specific fashion, and/or {@link #getResourcePatternResolver} for
 * extended pattern resolution.
 * 
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #getConfigResources
 * @see #getConfigLocations
 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 */
public abstract class AbstractXmlApplicationContext extends
		AbstractRefreshableApplicationContext {

	/**
	 * Create a new AbstractXmlApplicationContext with no parent.
	 */
	public AbstractXmlApplicationContext() {
	}

	/**
	 * Create a new AbstractXmlApplicationContext with the given parent context.
	 * 
	 * @param parent
	 *            the parent context
	 */
	public AbstractXmlApplicationContext(ApplicationContext parent) {
		super(parent);
	}

	/**
	 * 通过XmlBeanDefinitionReader载入Bean的定义.<br/>
	 * Loads the bean definitions via an XmlBeanDefinitionReader.
	 * 
	 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
	 * @see #initBeanDefinitionReader
	 * @see #loadBeanDefinitions
	 */
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory)
			throws IOException {
		// 为给定的BeanFactory创建新的XmlBeanDefinitionReader
		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(
				beanFactory);

		// Configure the bean definition reader with this context's resource
		// loading environment.
		beanDefinitionReader.setResourceLoader(this);
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		initBeanDefinitionReader(beanDefinitionReader);
		loadBeanDefinitions(beanDefinitionReader);
	}

	/**
	 * Initialize the bean definition reader used for loading the bean
	 * definitions of this context. Default implementation is empty.
	 * <p>
	 * Can be overridden in subclasses, e.g. for turning off XML validation or
	 * using a different XmlBeanDefinitionParser implementation.
	 * 
	 * @param beanDefinitionReader
	 *            the bean definition reader used by this context
	 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass
	 */
	protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
	}

	/**
	 * 为给定的XmlBeanDefinitionReader载入bean定义。<br/>
	 * Load the bean definitions with the given XmlBeanDefinitionReader.
	 * <p>
	 * The lifecycle of the bean factory is handled by the
	 * {@link #refreshBeanFactory} method; hence this method is just supposed to
	 * load and/or register bean definitions.
	 * 
	 * @param reader
	 *            the XmlBeanDefinitionReader to use
	 * @throws BeansException
	 *             in case of bean registration errors
	 * @throws IOException
	 *             if the required XML document isn't found
	 * @see #refreshBeanFactory
	 * @see #getConfigLocations
	 * @see #getResources
	 * @see #getResourcePatternResolver
	 */
	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader)
			throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		// 首先获得BeanDefinition的配置文件的资源，判断是否存在，如果存在在加载，然后获取配置文件的路径，判断是否存在，如果存在则加载。
		if (configResources != null) {
			// 从资源中加载
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			// 从给定的路径加载
			reader.loadBeanDefinitions(configLocations);
		}
	}

	/**
	 * Return an array of Resource objects, referring to the XML bean definition
	 * files that this context should be built with.
	 * <p>
	 * The default implementation returns <code>null</code>. Subclasses can
	 * override this to provide pre-built Resource objects rather than location
	 * Strings.
	 * 
	 * @return an array of Resource objects, or <code>null</code> if none
	 * @see #getConfigLocations()
	 */
	protected Resource[] getConfigResources() {
		return null;
	}

	/**
	 * Return an array of resource locations, referring to the XML bean
	 * definition files that this context should be built with. Can also include
	 * location patterns, which will get resolved via a ResourcePatternResolver.
	 * <p>
	 * The default implementation returns <code>null</code>. Subclasses can
	 * override this to provide a set of resource locations to load bean
	 * definitions from.
	 * 
	 * @return an array of resource locations, or <code>null</code> if none
	 * @see #getResources
	 * @see #getResourcePatternResolver
	 */
	protected String[] getConfigLocations() {
		return null;
	}

}
